William Liu

Formation and disruption of current filaments in a flow‐driven turbulent magnetosphere

Recent observations have established that the magnetosphere is a system of natural complexity. The co-existence of multi-scale structures such as auroral arcs, turbulent convective flows, and scale-free distributions of energy perturbations has lacked a unified explanation, although there is strong reason to believe that they all stem from a common base of physics. In this paper we show that a slow but turbulent convection leads to the formation of multi-scale current filaments reminiscent of auroral arcs. The process involves an interplay between random shuffling of field lines and dissipation of magnetic energy on sub-MHD scales. As the filament system reaches a critical level of complexity, local current disruption can trigger avalanches of energy release of varying sizes, leading to scale-free distributions over energy perturbation, power, and event duration. A long-term memory effect is observed whereby the filament system replicates itself after each avalanche. The results support the view that that the classical and inverse cascades operate simultaneously in the magnetosphere. In the former, the high Reynolds-number plasma flow disintegrate into turbulence through successive breakdowns; in the latter, the interactions of small-scale flow eddies with the magnetic field can self-organize into elongated current filaments and large-scale energy avalanches mimicking the substorm.

Nonlinear Geophysics: Why We Need It

Few geoscientists would deny that effects are often sensitively dependent on causes, or that their amplification is commonly so strong as to give rise to qualitatively new “emergent” properties, or that geostructures are typically embedded one within another in a hierarchy. Starting in the 1980s, a growing number felt the need to underline the absolute importance of such nonlinearity through workshops and conferences. Building on this, the European Geosciences Union (EGU) organized a nonlinear processes (NP) section in 1990; AGU established a nonlinear geophysics (NG) focus group in 1997; and both unions began collaborating on an academic journal, Nonlinear Processes in Geophysics, in 1994.

Effect of heat flux on Alfvén ballooning modes in isotropic Hall‐MHD plasmas

The magnetosphere undergoes a transition from a dipole-like to taillike structure in the antisunward direction. In this region, Alfven ballooning instability has been considered as a leading candidate to be responsible for the onset and expansion phase of observed impulsive substorms. We apply the generalized Ohms law in isotropic Hall-MHD equations and study the effect of heat flux on the ballooning modes under substorm circumstances. The set of partial differential equations is obtained for a general ballooning dispersion relation from which all classical Alfven waves and fundamental ballooning modes are recovered, e.g., the decoupled shear Alfven and magnetosonic modes, the classical ballooning instability in incompressible plasmas. In the absence of the heat flux, the ballooning mode is featured by the coupling of the two modes by the superposition of the independent Hall effect and the independent plasma inhomogeneity effect. By contrast, heat flux exerts its influence on the ballooning mode by updating the coefficients of the terms in the dispersion relation. The results expose that the growth rate (γBM) has two branches. If kp is β free, one branch shifts versus β, while the other branch is damped substantially by the heat flux, leading to a more stable ballooning mode; if kc is β free, one branch shifts little versus β, but the other one has higher γBM driven by the heat flux, leading to a more unstable ballooning mode.

DIVISION II / WORKING GROUP INTERNATIONAL COLLABORATION IN SPACE WEATHER

The IAU Division II WG on International Collaboration in Space Weather has as its main goal to help coordinate the many activities related to space weather at an international level. The WG currently includes the international activities of the International Heliospheric Year (IHY), the International Living with a Star (ILWS) program, the CAWSES (Climate and Weather of the Sun-Earth System) Working Group on Sources of Geomagnetic Activity, and Space Weather Studies in China. The coordination of IHY activities within the IAU is led by Division II under this working group. The focus of this half-day meeting was on the activities of the IHY program. About 20 people were in attendance. The Chair of the WG, David F. Webb, gave a brief introduction noting that the meeting would have two parts: first, a session on IHY activities emphasizing IHY Regional coordination and, second, a general discussion of the other programs of the WG involving international Space Weather activities.

MULTISCALE GEOSPACE PHYSICS IN CANADA

Abstract Geospace physics research is entering a new era in Canada. Although this development has been a poorly kept secret among the informed observers, there has not been, to date, an attempt to summarize these changes in a single source and convey to the scientific world the vision and potential of the new “Northern perspective”. In this paper we make a first attempt to fill this gap, without, however, claiming authoritativeness or completeness – such a claim would be defeated by the fast-paced development in Canada on many fronts. The new Canadian perspective is based on a keen awareness of the multiscale character of geospace, and on a realistic yet innovative outlook which integrates Canadas strengths into national efforts emphasizing the use of multi-instrument techniques to attack multiscale complexities in problems. We organize our discussion in four major sections: a description of the plan to enhance Canadas leadership position in ground-based geospace science, centered on the Canadian Geospace Monitoring program; a description of Canadas latest effort to achieve major breakthroughs in our understanding of geospace transition region dynamics, centered on the Canadian small satellite experiment ePOP; a description of Canadas participations in three major international geospace missions (THEMIS, SWARM, and AMISR); and, finally, a description of two potential new Canadian-led geospace missions, Ravens and Orbitals. We will integrate key scientific goals and strategies in our narrative about these missions, and use examples to illustrate the considerable potential of these Canadian efforts.